Support for arm64 build.

build/config/arm.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-if (current_cpu == "arm") {
+if (current_cpu == "arm" || current_cpu == "arm64") {
   declare_args() {
     # Version of the ARM processor when compiling on ARM. Ignored on non-ARM
     # platforms.
-    arm_version = 7
+    if (current_cpu == "arm64") {
+      arm_version = 8
+    } else {
+      arm_version = 7
+    }
 
     # The ARM floating point mode. This is either the string "hard", "soft", or
     # "softfp". An empty string means to use the default one for the
     # arm_version.
     arm_float_abi = ""
 
     # The ARM variant-specific tuning mode. This will be a string like "armv6"
     # or "cortex-a15". An empty string means to use the default for the
     # arm_version.
     arm_tune = ""
@@ skipping 43 matching lines @@
 
     arm_use_thumb = true
 
     if (arm_use_neon) {
       arm_fpu = "neon"
     } else {
       arm_fpu = "vfpv3-d16"
     }
   }
 }